Big Ideas Math Geometry, 2014
BI
Big Ideas Math Geometry, 2014 View details
Cumulative Assessment

Exercise 1 Page 718

Practice makes perfect
a We are told that the probability p that a randomly selected American is a sports fan is 63 % = 0.63.

p= 0.63 We randomly select n= 14 Americans to survey and we want to draw a histogram of the binomial distribution for that survey.

Are you a sports fan? YES NO

Recall that in a binomial experiment with n independent trials there are two possible outcomes, a success and a failure. The probability of success, which is the probability of a positive answer, equals p= 0.63. Conversely, the probability of a failure is denoted as 1- p. 1- p=1- 0.63 Now, for a binomial experiment, the probability of exactly k successes can be written with the following formula. Note that k successes is equivalent to k people saying they are sports fans. P(k successes ) = _nC_kp^k(1-p)^(n-k) In this formula, _nC_k can be expanded using a formula for the number of combinations. _nC_k ⇔ n!/k!(n-k)! Now, let's substitute n= 14 and p= 0.63 into our formula and simplify. P(k) = _(14)C_k( 0.63)^k(1- 0.63)^(14-k) ⇓ P(k) = _(14)C_k(0.63)^k(0.37)^(14-k) We need to calculate the probability of k successes for each possible value of k. Note that there can be as many as k=0,1,2,..., 14 successes in this trial. Let's use a table for this.

Number of Successes k P(k) Simplify Use Calculator
0 _(14)C_0(0.63)^0(0.37)^(14- 0) 1(1)(0.37)^(14) 0.000000
1 _(14)C_1(0.63)^1(0.37)^(14- 1) 14(0.63)(0.37)^(13) 0.000021
2 _(14)C_2(0.63)^2(0.37)^(14- 2) 91(0.63)^2(0.37)^(12) 0.000237
3 _(14)C_3(0.63)^3(0.37)^(14- 3) 364(0.63)^3(0.37)^(11) 0.001619
4 _(14)C_4(0.63)^4(0.37)^(14- 4) 1001(0.63)^4(0.37)^(10) 0.007582
5 _(14)C_5(0.63)^5(0.37)^(14- 5) 2002(0.63)^5(0.37)^9 0.025821
6 _(14)C_6(0.63)^6(0.37)^(14- 6) 3003(0.63)^6(0.37)^8 0.065949
7 _(14)C_7(0.63)^7(0.37)^(14- 7) 3432(0.63)^7(0.37)^7 0.128334
8 _(14)C_8(0.63)^8(0.37)^(14- 8) 3003(0.63)^8(0.37)^6 0.191200
9 _(14)C_9(0.63)^9(0.37)^(14- 9) 2002(0.63)^9(0.37)^5 0.217038
10 _(14)C_(10)(0.63)^(10)(0.37)^(14- 10) 1001(0.63)^(10)(0.37)^4 0.184776
11 _(14)C_(11)(0.63)^(11)(0.37)^(14- 11) 364(0.63)^(11)(0.37)^3 0.114407
12 _(14)C_(12)(0.63)^(12)(0.37)^(14- 12) 91(0.63)^(12)(0.37)^2 0.048700
13 _(14)C_(13)(0.63)^(13)(0.37)^(14- 13) 14(0.63)^(13)(0.37) 0.012757
14 _(14)C_(14)(0.63)^(14)(0.37)^(14- 14) 1(0.63)^(14)(1) 0.001551
We can now draw our histogram.
Histogram

Showing Our Work

Calculating _nC_k
As previously mentioned, there is a formula to calculate the value of _nC_k. _nC_k ⇔ n!/k!(n-k)! Let's calculate _(14)C_0 using this formula.
_(14)C_0
14!/0!(14-0)!
14!/0!14!
14!/0!14!
1/0!

0!=1

1/1
1
We found that _(14)C_0=1. Through following the same procedure, we can calculate the values of the other combinations.
b We want to find out what number of Americans participating in the survey are most likely to consider themselves sports fans. For that, let's take a look at the histogram form Part A.
Histogram
We see that the probability for k=9 is the highest. This means that the most likely outcome is that 9 out of 14 people in the group are sports fans.
c We need to find the probability that at least 7 Americans out of the group are sports fans. This means finding the probability that k is greater than or equal to 7.
P(k ≥ 7) Notice that the probability is a sum of the probabilities when the number of successes k equals 7, 8, ... ,14.

P(k ≥ 7) = P(7) + P(8) + ... + P(14) Let's use the probabilities we found in Part A.

k P(k)
0 0.000000
1 0.000021
2 0.000237
3 0.001619
4 0.007582
5 0.025821
6 0.065949
7 0.128334
8 0.191200
9 0.217038
10 0.184776
11 0.114407
12 0.048700
13 0.012757
14 0.001551

Let's add the probabilities. This will give us our answer. & 0.128334 +& 0.191200 +& 0.217038 +& 0.184776 +& 0.114407 +& 0.048700 +& 0.012757 +& 0.001551 =& 0.898763 We have that the probability that at least 7 Americans out of the group are sports fans equals approximately 0.899=89.9 %.